In 1954 the United States began serious nuclear testing in the
Pacific Ocean on the island of Bikini Atoll and they carried out the
detonation of a massive bomb codenamed Castle Bravo. This was the first
test of a practical hydrogen bomb and the largest nuclear explosion
ever set off by the United States. In fact, a bit like a ten year old
with a box of fireworks and some matches, they really had little idea
what they were doing and when it was detonated it proved much more
powerful than the boffins had predicted, and created unexpected
widespread radioactive contamination which has prevented people from
ever returning to the island.

Castle Bravo was the most powerful nuclear device ever detonated by
the United States, with a yield of fifteen Megatons. That yield, far
exceeding the expected yield of four to six megatons which, combined
with other factors, led to the most significant accidental radiological
contamination ever caused by the United States. In terms of TNT tonnage
equivalence, Castle Bravo was about one thousand, two hundred times more
powerful than each of the atomic bombs which were dropped on Hiroshima
and Nagasaki during World War II.